A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communications may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided include two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.
In a wireless communication system at least a part of communications between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). The wireless systems can typically be divided into cells, and are therefore often referred to as cellular systems.
A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and/or receive communications on the carrier.
Carrier aggregation can be used to increase performance, especially for example, for peak data rate. In carrier aggregation a plurality of carriers are aggregated to increase bandwidth. Carrier aggregation comprises aggregating a plurality of component carriers into a carrier that is referred to in this specification as aggregated carrier.
The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, it can be defined if carrier aggregation is used. Communication protocols and/or parameters which shall be used for the connection are also typically defined. An example of attempts to solve the problems associated with the increased demands for capacity is an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is being standardized by the 3rd Generation Partnership Project (3GPP). The various development stages of the 3GPP LTE specifications are referred to as releases. The aim of the standardization is to achieve a communication system with, inter alia, reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. A further development of the LTE is referred to as LTE-Advanced (LTE-A). The LTE-Advanced aims to provide further enhanced services by means of even higher data rates and lower latency with reduced cost.
A feature of the LTE-Advanced is that it is capable of providing carrier aggregation. In LTE-A two or more component carriers (CCs) can be aggregated in order to support wider transmission bandwidths, such as up to 100 MHz, and/or for spectrum aggregation. It is possible to configure a user equipment (UE) to aggregate a different number of component carriers connected with the same base station, for example a LTE eNode B (eNB), and of possibly different number of component carriers (aggregated bandwidth) in the uplink (UL) and the downlink (DL).
In a time division duplex (TDD) system, it is possible to provide specific TDD configurations for each aggregated component carrier. A problem that may occur in specific time division duplex configurations for each component carrier is that a communication device may be subject to self-interference. Furthermore, hybrid automatic repeat requests timing may be different for different TDD configurations which can make carrier aggregation difficult.